314 



PHOTOSYNTHESIS 



been saturated with carbon dioxide, the amount of this gas evolved on 

 acidification was 17.3 mg. Similarly, when the precipitate was dialyzed 

 and again precipitated this, after being in a carbon dioxide- free atmosphere, 

 evolved 28.6 mg. on acidification, and after saturation with carbon dioxide, 

 evolved 56.6 mg. In Table 32 are given some of the results obtained 

 with different leaf material. 



TABLE 32 



Carbon Dioxide Evolved (mg.) from 1 Gram Dried and Powdered Leaves and 



FROM Alcoholic Precipitates Obtained by Extracting the Dried Leaves 



WITH Ether-Water and Precipitation with 95 Per Cent Alcohol. 



In Each Case a Quantity of Water Was Added to the Dry 



Preparations Equivalent to that Originally Present 



IN THE Fresh Leaves. Determinations Made with 



the Van Slyke Blood Gas Apparatus. 



After Being 



in C02-Free After 



Original Atmosphere Saturation 



Material Condition for 4 Hours with CO2 



Sunflower 13.9 mg. 13.7 mg. 27.7 mg. 



Nettle 6.2 5.9 12.7 



Spinach 0.2 0.0 0.7 



Hydrangea 0.1 0.1 0.2 



Turnip 0.5 0.3 0.5 



Alfalfa 0.4 0.2 0.3 



Rhubarb (leaves) 0.02 0.0 0.02 



Grass 0.1 0.1 0.6 



Ramilina recticulata 0.0 0.0 0.2 



Sunflower ale. ppt — 24.4 49.5 



An examination of Table 32 will show that the sunflower and nettle 

 leaves occupy a peculiar position in regard to their capacity to absorb 

 carbon dioxide. Moreover, a comparison of the values obtained for the 

 evolution of carbon dioxide, on acidification, after the preparation had 

 been in a carbon dioxide-free atmosphere and after saturation with car- 

 bon dioxide, show that the former is very close to one half the latter. 

 This is what would be expected if the absorption were due to an inorganic 

 carbonate. The same relation holds for the alcoholic precipitates ob- 

 tained from water-ether extracts of the dried leaves. When the latter 

 are dialyzed and the dialysate is again precipitated with alcohol, the absorb- 

 ing capacity and the ash content of the latter are considerably higher than 

 the original precipitate, though the carbonate : bicarbonate ratio still main- 

 tains. There is, however, no direct relation between the absorption capac- 

 ity and the amount of ash in the leaves and alcoholic precipitates. It 

 is, of course, possible that all leaves have an absorption capacity for 

 carbon dioxide, but from these results it would appear that with many 

 this is very small. Certainly it is not justifiable to draw conclusions from 

 the behavior of the sunflower and nettle as to the behavior of all plants. 

 Whether, finally, this absorption capacity for carbon dioxide has any 

 direct relation to the photosynthetic process will require special experi- 

 ments. It is suggestive, at least, that both the sunflower and nettle 

 are Imown as possessing a high photosynthetic activity. 



